It has for ages been known, that for preparing coffee different devices and methods could be applied, where the perspective reaches from a blue, enamelled jug with matching fabric bag to espresso devices, where steam under high pressure is lead through the ground coffee beans. From approximately mid 1970'es a piston coffee maker has been known and widely distributed in Denmark, and such piston coffee makers have been made in varying sizes covering expected needs from 3 and up to 12 persons.
From U.S. Pat. No. 1,346,485 a device for preparing small amounts of beverages, such as coffee or tea, is known to have a container being enclosed by a heat insulating casing, which is composed of a lower portion and a cover portion. Here the container and the casing are made of different materials and are therefore made in individual processes, thereby creating problems of fitting together and tolerances. Such production is expensive as partly a large percentage of loss can be anticipated, and partly a large staff is needed for handling and quality control.
From U.S. Pat. No. 5,809,867 it is known to dress the container with an isolating jacket. Also here, the container and the jacket are made of different materials and are therefore made in individual processes, thereby creating problems of fitting together and tolerances. Like the previous mentioned state of the art, the manufacture is expensive with a large percentage of loss and a large staff needed for handling and quality control.
It has never been possible--even in small piston coffee makers--to prepare smaller portions of coffee, as the dimensions result in an unfavourable relation between the total surface and the volume of the infusion fluid, taking into consideration that Stephan-Bolzmanns law for temperature emission, where the radiated energy through a surface is reversed proportional to the volume of the body and proportional with the area of the surface and with the absolute temperature in fourth power, is also valid for such small bodies. This has, until now--including the mentioned state of the art, caused that the infusion fluid during the preparation delivered a large amount of the heat to the environment, whereby the temperature diminished before the coffee had delivered its aromatic compounds to the infusion fluid. This has obviously been to the disadvantage of drinking the coffee. Further, it has been uneconomic to produce a piston coffee maker for only one person, as the expenses for that have been exorbitant, as tools, assembling and packaging by and large are independent of the size of a piston coffee maker.